Maybe not, it _might_ cause obesity: https://slimemoldtimemold.com/2021/10/11/a-chemical-hunger-i...
It's interesting that this downside wasn't even on the radar of this article in 2011, and indeed no serious consideration of possible downsides was presented at all, just a snide dismissal that "anyone who has tangled with the anti-fluoride campaign will realise that lithium lobbyists will have a long, hard road to travel."